Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac rhythm management devices such as implantable pacemakers and implantable cardioverter defibrillators (ICDs). The devices are used to treat patients using electrical therapy and to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include electrical leads in communication with sense amplifiers to monitor electrical heart activity within a patient, and often include sensors to monitor other internal patient parameters. In general, the sensors convert sensed internal parameters into electrical signals. The electrical signals monitored within the patient and the electrical signals from the sensors can be quantized by analog-to-digital converters and stored in the IMD as data.
Implantable medical devices are able to communicate with external devices using wireless communication methods. The external devices are often external programmers that use wireless communication links to change performance parameters in the implantable device. The implantable device also wirelessly transmits the stored data to an external device. The external device may then display the collected data on a computer screen display or a strip chart recorder.
The IMDs are also able to detect events, such as by monitoring the electrical heart activity signals. In a cardiac rhythm management device, these events can include heart chamber expansions and contractions. The IMD identifies such a detected event by generating a marker for transmission to the external device. This marker is usually in the form of a binary code. Transmitting such a binary code allows the external device to label an event on the screen display or strip chart recorder.
As technology used in implantable medical devices advances, the devices will be able to collect data from multiple leads and multiple sensors from multiple locations. They also will detect events occurring from such multiple sources. Potentially, this results in a large amount of data to be collected by the implantable device and transmitted to the external device. Additionally, the data may be collected from different types of sensors at different times and/or sampling rates, or processing may be done on the collected data by the implantable device before the data is transmitted to an external device. Thus, the relative timing between the events and the data as displayed at the external device is often different from the relative timing of the events and data as they actually occur.
The large amount of data coming from various sources complicates the task of reconstructing the information for a display while preserving the correct timing relationship among the data and markers. What is needed is an improved method of managing data that is available from implantable medical devices.